Astronomy Picture of the Day
January 2, 2013

On the Edge of Ailey Crater
On the Edge of Ailey Crater

Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington and Dr Paolo C. Fienga/LXTT/IPF for the additional process. and color.

In this image, taken by the NASA - MESSENGER Spacecraft during last month of December, 2012, we can see an interesting portion of the Impact Crater named Ailey (located in the Middle Latitudes of the Northern Hemisphere of Mercury and whose diameter is about 20,5 Km - such as approx. 12,7 miles). If you look carefully to the upper right (Dx) side of the frame, you will be able to clearly see some fresh and bright Material that has - probably in "recent" geological times - been exposed in the Crater Walls, and whose color and brightness makes it stand out in the whole scene, by way of creating a sharp contrast with the darker and relatively smooth Ejecta and Impact Melt that has ponded just outside the Rim of Ailey Crater, but still within the borders of the older Impact Crater that Ailey itself overprints.

Note: as far as the color of the Surface of Mercury is concerned, some Readers wrote us asking the reason why we, as IPF, are used to show it so dark, and - in certain areas - reddish, while the color pictures published by NASA show the Surface of Mercury - in general and almost all the times - as very bright (mostly gray, with various shades of the same color), with very little red and other colors (which basically means that the pictures of Mercury published "in Natural Colors" by the People of NASA, end up by being, quite often - if not always - almost monochromatic).

Well, the answer to this interesting question can be found in the circumstance that Mercury, in our opinion, since it does not possess neither an Atmosphere, nor a Magnetic Field that is fit (---> capable) to protect its Surface from the so-called "Space Weathering", must have suffered - for several billions of years - a powerful and continuous bombardment of Charged Particles (Solar Wind and Cosmic Rays) whose one of its main effects (like we have learned by observing and studying the Asteroids, as well as the airless moons of the four Gas-Giant Planets) is to "erode" (in a manner of speaking) said Surface, and, in time, to darken it up until an almost solid black color - with, sometimes, reddish nuances - is reached.

Said that, we noticed, on the other hand, that the pictures of the Planet Mercury (as well as of many other airless Rocky Celestial Bodies, like, for instance, the Giant Asteroid 4-Vesta and the airless moons of Jupiter and Saturn) which have been published by the NASA People on their beautiful Planetary Photojournal (or elsewhere on the NASA pages), quite often, if not always, tend to be slightly (or even highly) overexposed and not balanced towards a "Human Vision" of the targeted objects. In other words (and in our humble opinion, as IPF), with the aim of showing more details of the pictured Surface Features of Mercury (as well as of any other, we repeat, airless Rocky Celestial Body of the Solar System) and, at the same time, in order to make these Surface Features look a little "nicer" to the untrained eye (and/or, most likely, to make them easier to be seen and interpreted even by NON-Specialists of this Subject Matter), the NASA People have sacrificed the visual accuracy (from a "human point of view") of the Real Colors (and relevant Albedoes) that actually characterize them.

Please remember that the Real Visible Colors of the targeted Celestial Bodies and their Surface Features are those Colors that we, as IPF, have decided to call Absolute Natural Colors (---> meaning the colors that a Human Eye AND NOT AN ELECTRONIC EYE - like a CCD Camera - would actually perceive if someone were onboard the NASA - MESSENGER Spacecraft (or any other Spacecraft in charge of taking orbital pictures of a given Celestial Body) and then looked down, towards the Surface of Mercury (or Mars, or 4-Vesta, et cetera). Of course, your opinions and insights even (still about this subject, as well as regarding any other subject you may be interested in), are and will always be deeply appreciated.

Date acquired: December, 8th, 2012
Image Mission Elapsed Time (MET): 263440024
Image ID: 3100214
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 45,68° North
Center Longitude: 177,7° East
Resolution: 22 meters/pixel
Solar Incidence Angle: 46,3° (meaning that the Sun, at the time that the pictures were taken, was about 43,7° above the imaged Local Mercurian Horizon)
Emission Angle: 2,6°
Sun-Mercury-Messenger (or "Phase") Angle: 46,2°

This picture (which is an Original NASA - MESSENGER Spacecraft color frame published on the NASA - Planetary Photojournal with the ID n. PIA 16640) has been additionally processed and then re-colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - MESSENGER Spacecraft and then looked down, towards the Surface of Mercury), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among other things, the existence of different Elements (Minerals) present on the Surface of Mercury, each having a different Albedo (---> Reflectivity) and Chemical Composition.

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